1. Field of the Invention
The subject invention relates to a mount assembly for a vehicle wherein the mount assembly isolates vibrational and/or translational movements between a frame of the vehicle and a vehicle body.
2. Description of Related Art
Mount assemblies for vehicles are well known in the art. Examples of such assemblies are shown in U.S. Pat. Nos. 5,799,930 and 6,361,096. Each of these assemblies include a steel carrier having one or more insulators. The carrier and insulators are mounted between a frame of a vehicle and a vehicle body in order to isolate movement between the frame and vehicle body. The insulators are typically formed of an elastomeric material such as rubber or microcellular polyurethane (MPU).
The stiffness of the insulator is based on material stiffness (modulus of elasticity) and geometry. As such, one important factor in the development of mount assemblies relates to the modulus of elasticity, also known as a spring rate, of the insulators. The insulators can have a relatively soft spring rate, which is preferred for isolating vibrational motion. Vibrational motion is generally associated with lower amplitudes and higher frequencies, such as when a vehicle travels over typical undulations of a road surface. It is desirable to have the insulators operate at lower or softer spring rate to allow for improved isolation and cushioning of the vibrations of the frame relative to the vehicle body.
On the other hand, the insulators can have relatively stiff or hard spring rates, which is preferred for controlling translational motion. Translational motion is typically associated with high amplitude, lower frequency events such as impacts, which can define a maximum displacement of the frame relative to the vehicle body.
In order to achieve the desired cushioning performance, prior art insulators are at times formed of a material having a low modulus of elasticity, such as microcellular polyurethane (MPU). Although, these MPU insulators can provide the soft spring rate as well as some maximum displacement control, the total maximum displacement is sometimes still too large and the nature and location of the transition from soft to hard spring rate cannot be controlled independent of the properties of polymer. Thus these types of insulators are not easily tunable. Also, soft insulators, such as MPU, can have a relatively large height, which require large clearances between the carrier and the frame. This also creates an undesirable large displacement between the carrier and the frame during translational motion which equates to an undesirable large movement (maximum displacement) between the frame and the vehicle body. Further, MPU is more difficult to mold and thus provides limited choices of geometry.
In order to overcome some of the above disadvantages, the prior art has contemplated forming insulators of materials having different modulus of elasticity. These insulators are a compromise between softer spring rates, to isolate vibrations, and higher spring rates, to isolate impacts. For example, U.S. Pat. Nos. 4,286,777 and 6,419,215, discloses an insulator formed of two materials having different modulus of elasticity. The advantage of this type of insulator design relates to the tuneability or customization of the insulator for a particular application. However, the conventional insulators still have significant limitations and typically cannot be adequately customized or tuned. As such, there remains an opportunity to further develop the material and geometrical features of the mount assemblies.
Accordingly, it would be desirable to develop a mount assembly that is of a reasonable height, takes advantage of a low or soft spring rate, has low maximum displacement, and is easily tunable or customizable.